Phytochemical content, cellular antioxidant activity and antiproliferative activity of Adinandra nitida tea (Shiyacha) infusion subjected to in vitro gastrointestinal digestion

Adinandra nitida tea (Shiyacha) is a traditional eminent and flourishing tea with a long history in Southeast Asia. However, transformation of phytochemicals of A. nitida tea infusion during in vitro simulated digestions is vague. Herein, we investigated cellular antioxidant and antiproliferative activity of phytochemicals obtained from A. nitida tea infusion subjected to in vitro gastrointestinal conditions. Phenolic, flavonoid, flavonol, and anthocyanin contents found in A. nitida tea infusion were evaluated by normal colorimetric methods. Subsequently, the main compounds were determined by high-performance liquid chromatography. The antioxidant activity was evaluated based on peroxyl radical scavenging capacity (PSC), oxygen radical absorbance capacity (ORAC), and cellular antioxidant activity (CAA). The antiproliferative activity towards Caco-2 cells was determined by the cell methylene blue colorimetric assay. It was found that in simulated gastrointestinal fluids, the contents of phenolics and flavonols increased, whereas the contents of flavonoids and anthocyanins decreased. Moreover, the content of (-)-epigallocatechin and camellianin B increased, whereas that of L-epicatechin, quercitrin, and camellianin A decreased. Furthermore, the oxygen radical scavenging capacity and cellular antioxidant activity values increased, whereas the PSC values decreased. Most importantly, the gastrointestinal fluids of A. nitida tea infusion exhibited a strong antiproliferative activity towards Caco-2 cells and affected caspase 3/9 signaling pathway, and apoptosis induction might serve as the underlying mechanism for this antiproliferative activity. It can be concluded that A. nitida tea infusion may act as a potential intracellular antioxidant and colon cancer cell proliferation inhibitor.